This invention relates to automatic reproducing apparatus and in particular to sheet feeding and registration apparatus. Specifically, the present invention is directed to a simple mechanical actuation mechanism for a sheet separation, registration and feeding apparatus.
The development of automatic reproducing machines and, in particular, electrostatographic copiers has most frequently involved the use of paper feeding and registration systems using a set of pinch rolls or two pinch rolls with a stop or registration gate. These systems typically involve the application of high normal forces to the stack of sheets to insure separation and the feeding in the forward direction of the topmost sheet. In addition, with these systems, the topmost sheet is typically driven into contact with the stop of registration member to first register the lead edge of the sheet prior to the sheet being fed to the imaging or image transfer station. While the lead edge is constrained during this registration operation, the high normal force feeders continue to feed the sheet in the forward direction creating a buckle within the sheet and increasing the possibility of damaging the lead edge of the sheet by way of tearing or wrinkling as it is continuously driven into a stop surface. Furthermore, after the top sheet has been separated from the stack of sheets, some systems interrupt the driving motion of the feed rolls to reduce the possibility of damage to the a sheet are relatively complex and costly. However, perhaps the most significant difficulty with these systems is that a chamber must be made available for the sheet being registered against the stop to buckle without wrinkling. This is particularly significant in the design of small copiers which typically attempt to maximize the use of space to keep the overall volume of the copier to a minimum.
An alternative to the high normal force sheet feeders are the inertial feeders which have a high acceleration and a low normal force on the top sheet being fed. In this type of feeding arrangement, devices are used to continuously urge the top sheet in the stack in a forward direction with relatively high acceleration but with relatively low normal force and therefore reduce possibility of damage. Typical of such inertial feeding devices are the continuous rotating flexible paddle wheel feeders. In these devices, as soon as the trailing edge of the top sheet in a stack of sheets clears the feeding device, the second and next successive sheet is fed forward. If the top sheet is being registered further down the sheet feeding path or if the top sheet has just cleared a nearby retracted registration stop member, there is the possibility of the second sheet being fed along with the top sheet beyond the registration edge. One way of avoiding this is to interrupt the feeding motion of the paddle wheel feeder, for example, with a clutch for every sheet being fed. Such clutch driven systems are more complicated and expensive to manufacture and maintain. The inertial sheet feeders provide a good choice for small compact copiers since they are relatively simple and inexpensive and require very little machine volume.
One way to classify small compact copiers is with regard to the position of the document during imaging. Some copiers have a flat, stationary document platen and a scanning optical system to transmit the image of the intelligence on the document to the imaging surface. Other copiers use a moving platen arrangement which transports a document past a stationary optical system which transmits the image to the imaging surface. In the first group of machines the actuation of the sheet feeding and registration mechanism is typically tied to the movement of the optical system through the use of some complex mechanical or electromechanical device. In this latter group of machines, the feeding of the copy paper is tied into, or somehow synchronized, with the feeding of the document. The problem sought to be solved with these devices is how to timely actuate the paper feed and registration system together with the document transport system. Various electrical and electromechanical arrangements have been used for this purpose. Typical of the systems proposed are those which sense the leading edge of the document being transported and together with some timing device actuate the paper feeder which itself may be driven through an electromagnetic clutch arrangement. Such systems are both complex and expensive and add to the overall manufacturing time and cost.